About once a week, a patient comes to see sleep expert Dr. Catherine Darley with a startling – and scary –admission: they fell asleep while driving.

"When I talk about drowsy driving, the hairs on my arms stand up," said Darley, who specializes in natural medicine from her office in downtown Seattle. "It's freaky."

Recent national surveys from the National Sleep Foundation suggest one out of every three drivers admits to actually falling asleep behind the wheel.

In Washington state, the latest data suggests 10 to 12 people a year die as a result of drowsy or sleepy driving crashes, according to the state's Department of Transportation.

"I've even had people say they've fallen asleep at stop signs," said Darley.

So what can you do?

For starters, pay attention to how much sleep you need each night. It may be more than eight hours.

Darley says sleep needs are individual – some people need more than others to be well-rested and functional.

You should also avoid driving between 2 p.m. and 5 p.m. or so. These are the hours when your body's circadian rhythm naturally encourages you to become drowsy and tired, even if you've had enough sleep.

Here are some additional tips from Darley:

- Get the sleep you need the night before by planning and packing for your trip ahead of time
- Talk with a passenger who can monitor your alertness and switch drivers regularly
- Take a break to get out of the car and walk around every two hours or 100 miles
- If you feel drowsy, pull over someplace safe to nap for 20 minutes
- Strategically have some caffeine to boost alertness; it will take about 20 minutes to take effect
- Limit driving during your normal sleep hours
- Avoid alcohol
- Opening the window or turning up the radio have not been shown to improve drowsy driving